Resource: decode_hour

Resource

decode_hour

Command Line

-dh=hour[:min][-pre+post]

Environment Variable

wxpdecode

Default Value

The same hour as original file

The decode programs need to know the hour to decode to eliminate data which is too far
from the requested time. By default, the decoder uses the specified time form either
the filename or current resources. Sometimes this
is not the time requested for decoding. A good example of this is upper air data.
In some cases, upper air data for a particular hour is located in 3 to 4 hourly
files (11,12,13 and 14Z). To decode this range, the following can be used "uacvt
-cu=la -ho=-212 -nh=-3" but this will use 14Z as the decode hour and of
course this will decode little. The decode_hour
resource solves this problem, disconnecting the decode hour from the other resources.
The correct way to decode this data is:

uacvt -cu=la -ho=-212 -nh=-3 -dh=-12

The "-12" on the decode hour specifies to use the nearest 12
hourly file. If the number is positive, it would only decode 12Z data and not 00Z
data.

Also with upper air and synoptic data, there needs to be a way of including data from
surrounding hours. By default, if 12Z synoptic data is decoded, smcvt
will only decode 12Z reports. The problem is that some places like Australia report
at off hours such as 11 and 23Z and thus these reports would not be included.

Decode Time Ranges

The decode_hour resource allows the user to specify the time range in
minutes where data is valid. This varies from decoder to decoder. For surface data, this
will be -15 to +10 minutes. For upper air data, this will be -2 to +2 hours. With the pre
and post parameters, the exact range before and after the decode time can be set.
Any data outside this range will be decoded but not saved to the output file.
The syntax for the decode hour and range is:

-dh=hour:min-pre+post
-dh=hour-pre+post
-dh=:-pre+post

where hour and min can be replaced with "cu"
for current data based on the filename or current
resource (not based on clock time). In addition, the hour can be replaced with
"cu-hour". The pre and post
values are in minutes around the decode time. For example, to change the METAR
decode time to 20 minutes after the hour with a range of +/- 10 minutes:

sacvt -cu=la -dh=cu:20-10+10

If the previous hours data needs to be converted but using 3 hourly files including the
current and the previous two:

sacvt -cu=la -dh=cu-1 -nh=-2

If the current time is 19Z, this would decode the 17, 18 and 19Z file to decode the 18Z
data.